Oleo device for landing gears and the like



Jan. 2, 1940. 'r. DE PORT CLEO DEVICE FOR LANDING GEARS ANDTHE LIKE Original Filed April '27, 1931 INV EN T OR 7;-IEOPHILE DE PORT k Z MQ fi I ATTO NETS Patented Jan. 2, 1940 UNITED STATES PATENT OFFICE Thopliile de Port, New Carlisle, Ohio Original application April 27, 1931, Serial No.

Divided and this application December 21, 1931, Serial No. 582,362

6 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The invention relates to improvements in the method of absorbing and dissipating the kinetic energy of resiliently suspended bodies and particularly to landing gear for airplanes and other aircraft.

My invention contemplates the use of a shock absorber in the oleo leg or strut of the landing gear of the type in which a liquid is forced, from one place to another by the relative movement of the airplane body and the axle of the landing member, and thereby serving as the resisting medium for dissipating the kinetic energy of the airplane body and therefore cushioning the shocks.

It is well-known that, in accordance with the laws of mechanics, there is a theoretical minimum impact load consistent with a given energy to be dissipated in a given length of movement. It is very desirable in aircraft landing gear or other shock absorbing devices that the kinetic energy be dissipated in the shortest possible movement of the device and that the impact load, consistent with that movement, be approximately that of the theoretical minimum.

Heretofore in airplane landing gear having resilient wheels or tires and shock absorbing devices of the character in which a metering orifice 'or a metering pin is employed, the piston would have to move a considerable distance prior to obtaining a piston velocity consistent with a pressure corresponding to a predetermined maximum load on the resilient wheel or tire under the corresponding deflection.

In an oleo shock absorber the velocity of the piston is known to increase from zero to its maximum speed and then to decrease again to zero. It is moreover known that the higher the piston speed and the smaller the orifice, the larger will be the load on the piston. The most efiicient type of oleo shock absorber is one in which the load on the piston is constant throughout its entire stroke. The maximum efliciency is obtained when the maximum load on the piston is maintained throughout the entire stroke. In accordance with my invention I have provided means whereby the relative movement of the piston and cylinder is substantially restrained against movement during the initial building up of the loads on the tire until the tire has been deflected to a predetermined maximum value depending upon the given energy to be dissipated by conversion into heat energy, during which time the piston has moved relative to the cylinder 'a relativelyshort distance, but has reached its maximum velocity consistent with the maximum load. From this point of the stroke of the 5 piston, the impact energy is gradually dissipated and the piston velocity gradually decreases to zero, while the tire is kept substantially deflected until the bulk of the energy is dissipated. In order to reach the maximum efficiency of the 10 shock absorber it is necessary to reach the maximum load without expending any appreciable part of the available piston stroke and then to maintain this load constant throughout a major portion of the stroke. To this end the ratio of 15 area of the piston to the area of the orifice is gradually increased so that the load is maintained constant.

It is, therefore, the'primary object of my invention to provide an improved method of dis- 20 sipating the energy,'due to the vertical velocity during landing of an airplane having a resilient suspension medium of given characteristics and an energy dissipating medium, by causing the'resilient suspension medium of the airplane, such 25 as the tire of the landing member, to be deflected to a predetermined degree, thereby storing a part of the kinetic energy; simultaneously building up the impact load to substantially its maximum during the deflection of the suspension 80 medium, by restricting the airplane from moving relative to the ground except for the tire deflec tion, or relative to the axle of the landing member; and, thereafter dissipating the energy with-- out increasing the impact load consistent with 85 the predetermined deflection of said tire.

, The principle of the invention may be best understood by reference to the following description of several illustrative embodiments thereof shown in the accompanying drawing, wherein:

Fig. 1 is a front elevational fractional view of an airplane showing only one complete half of landing gear embodying my invention;

Fig. 2 is a vertical sectional view of my novel oleo leg;

Figs. 3, 4, 5 and 6 are four views of the oleo leg and tire arrangement at diiferent consecutive stages respectively in landing, the oleo leg being shown in section; and

Figs. '7 and 8 are fractional views of further 0 modiflcationsoi my invention.

Referring to the drawing, the illustrative oleo leg 8, shown in Figs. 2 to '6 embodying one form of my invention as applied to a conventional landing gear 0 of a monoplane (Fig. l), is connected I at its lower end to a wheel l2 through the axle end portion 14 of a strut member I 6, the upper end of the oleo leg being secured in the conventional manner to the airplane wing, preferably by a ball and socket joint.

Pneumatic means, such as a pneumatic tire l8 mounted on the wheel I 2, constitutes the resilient suspension medium for normal taxiing of the airplane and-cooperates with a shock absorber or damper 20 to check or absorb the shock of the airplane when landing. The shock absorber forms a part of the oleo leg 8 that extends substantially vertically and is hingedly connected at its lower end to the axle portion iii of the strut member by means of a strap 22, the strap 22 being provided with a split socket 24 that receives a lug 26 rigidly secured to the oleo leg at the lower end thereof.

The shock absorber, as illustrated in Figs. 2 to 6, comprises preferably a cylinder or other appropriately shaped chamber 28, having heads 30 and 32, the former being apertured to receive a hollow cylindrical plunger rod 34, the, latter being provided with an exterior downward projection 36, to which is rigidly connected an extension'38 of suitable length.

Within the cylinder 28 is a plunger 40 having an upwardly projecting hollow fitting 42 that is threaded to the open end of the plunger rod 34 determined height depending upon the relative internal volumes of the available space for the displacement of liquid in the oleo leg when the oleo leg is extended and compressed as shown in Figs. 3 and 6 respectively. This liquid which forms the resisting medium of the shock absorber, is permitted to pass upwardly from the cylinder chamber on the lower side of the plunger, through the passage 44 into the plunger cylinder 48 as the plunger moved downwardly and through a plurality of passages 50 into the cylinder chamber on the opposite side of the plunger; and is controlled in its passage by means of the metering pin that is centrally vertically disposed within the cylinder chamber, one end of which is fixedly secured within a threaded opening 52 of the head by a set nut 54, the other end of which is disposed within the passage 44. The passage is preferably formed with rounded edges or stream-lined to effect a laminar flow of the liquid and thereby prevent a foaming of the liquid.

The metering pin 46 is formed at its upper end with a bullet-shaped or stream-lined head 56 having the base portion thereof of predetermined uniform cross-sectional area-for a predetermined length and with a calculated or predetermined frustro-conically tapered body portion 58 that gradually diverges from a point substantially at the inner end of the head 56 and which may extend to the lower end or base of the pin; the head 56 being stream-lined to maintain the laminar flow of the liquid. In the neutral or inoperative position of the shock absorber the bullet-shaped head of the metering pin is disposed in the passage 44, providing therewith a restricted passage for the flow of liquid into the plunger rod cylinder, the walls of which are sufliciently spaced from the stream-lined end portion of the head 56 to permit relatively restricted flow of fluid for a predetermined distance in the relative movement of-the plunger and pin and thereby build up an impact load substantially equal to the maximum allowable impact load in a relatively short distance. Preferably the metering pin is formed with an abrupt frustro-conical taper that converges from the inner end of the bullet-shaped head towards the point where the tapered body portion 58 begins.

Theoretically and in accordance with my invention, the desired maximum impact load is obtained when the plunger movement is resisted by the flow resistance of liquid through a restricted orifice of substantially uniform crosssectional area for a length equal to the distance between the normal position of the plunger and pin and the position of least cross-sectional area of the abrupt frustro-conical portion of the pin. However, it has been found that the desired maximum impact load may be reached at a point along the metering pin short of the theoretical distance, thus by the time the plunger has moved the entire theoretical distance, the impact load will have been in excess of that desired and it might result in structural failure. Therefore, as a measure of safety, although it may mean the obtaining of a load slightly less than that desired, the metering pin is provided with the above-referred-to abrupt frustro-conical taper found by experience to give the best results.

The plunger 40 has a sliding fit with the walls of the cylinder 28 and is provided with two or 'more circumferential grooves-68 so as to trap liquid seepage and thereby form a seal.

The operation of this embodiment of my invention is as follows:

It will be seen from an inspection of the several stages in the operation of the landing gear illustrated in the drawing, that so long as the airplane is off the ground the piston or plunger 40 and cylinder 28 are in an extended position with the bullet-shaped end 56 of the metering pin disposed within the passage 44 of the plunger to provide a relatively restricted opening so that during the initial impact of the landing on the ground the plunger will encounter a practically solid liquid body; thus the pneumatic suspension medium, such as the air in the tire, will be compressed and the tire deflected as shown in Fig. 4 to a predetermined extent. During this period of deflection of the tire, the impact load of the airplane will have been built up to the desired maximum, a part of the kinetic energy of the airplane will have been absorbed by the pneumatic suspension and the plunger by a metering of the liquid through the restricted opening will have moved from a point along the bullet-shaped head to slightly beyond-the inner end thereof, a distance corresponding to the time required to deflect the tire to apredetermined extent and to simultaneously build up the impact load to the desired maximum. Thereafter the tire remains deflected under the maximum impact load as the remainder of the kinetic energy is being dissipated by the metering of the liquid, as the plunger moves along the tapered body portion 58 of the pin, which, as heretofore described, is calculated to maintain this predetermined or maximum allowable load on the oleo leg substantially constant throughout the major part of the stroke, while the velocity 01' the plunger is deaisasoa v creasing. Toward the end of the downward stroke of the piston successive loads on the tire corresponding to successive deflections decrease as successive loads on the plunger decrease due to the continued metering of the flow of liquid as the plunger moves downward. Thus the stored energy on the pneumatic suspension medium will have been dissipated in the last part of the stroke of the plunger and the static equilibrium between the weight of the airplane and the load on the tire equal to the weight is established.

The modifications of my invention, as shown in Figs. '7 and 8, embody the same principles as above described, except that the predetermined length of relatively restricted or throttled opening formed by protruding the stream-lined head of the metering pin within the port of the plunger, as shown in Fig. 2, is obtained by merely reversing the relationship of the plunger port and metering pin head. That is to say, in Fig. 7 the port 62 is provided with a cylindrical portion 64 of predetermined length to give the required effective longitudinaldimension and the longitudinal dimension of the cross-section of the pin 66 which cooperates with the port to provide constant restricted areas for a predetermined length in their relative movement, 'is

negligible.

In Fig. 8 both the head of the metering pin 68 and the port III of the plunger 12 may be provided with cylindrical portions having longitudinal dimensions I4 and 16 respectively for this a purpose, but in this case the combined longitudinal dimensions of these portions are equal to the predetermined eflective longitudinal dimension of the cylindrical portion of the pin head shown in Fig. 2 or of the port shown in Fig. 7.

-It is to be understood that my invention is not limited to the forms which are shown in the drawing, but that various changes may be made without departing from the spirit thereof.

This is a division of my co-pending application Serial No. 533,110, filed April 27, 1931, Oleo device for landing gear and the like. What I claim as new and desire to secure by Letters Patent is:

1. A method of absorbing energy during landing of an airplane comprising the steps of opposing an abruptly increasing resistance to the initial shock of landing, opposing a prolonged constant resistance after the initial landing shock, and opposing a decreasing resistance at the end of the landing shock.

2. A method of absorbing the energy of an airplane during landing comprising permittingthe load on the landing gear to rise relatively abruptly to a desired peak, then maintaining the load substantially constant and at the last of the absorption cycle reducing the load to permit the tire on the airplane to return to substantially its normal position under the weight of the airplane before the end of the absorption cycle.

3. The method of absorbing and dissipating the kinetic energy of a moving mass by the combined action of a. resilient energy-absorbing medium and an energy-dissipating medium, comprising the steps of building up in both said media a maximum impact load, not in excess oi! the maximum allowable impact load, during the initial load-producing movement of said mass to an extent corresponding substantially to the deflection of said resilient medium for said built up the kinetic energy of a moving mass by the combined action of a resilient energy-absorbing medium and an energy-dissipating medium, comprising the steps of building up in both media a maximum impact load, not substantially in excess of the maximum allowable impact load, during the'initial load-producing movement of said mass to an extent approximately equal to the deflection of said resilient medium for said built up maximum load and then decreasing the load during the remaining movement to a value equal to the weight of the mass, by resisting the load-producing movement of the mass while converting the unabsorbed and, absorbed kinetic energies into heat energy.

5.The method of absorbing and dissipating the kinetic energy of an airplane during landing by the combined action of a resilient energyabsorbing medium and an energy-dissipating medium carried by said airplane, comprising the steps of building up in both said media a maximum impact load, not in excess of the maximum allowable impact load during the initial loadproducing movement of said airplane to an extent corresponding substantially to'the deflection of said resilient medium for said' built up maximum load, thereby absorbing part of the kinetic energy, of then maintaining said load substantially constant throughout a major portion of the remaining load-producing movement of said airplane by resisting the load-producing movement at a substantially constant deceleration while converting the unabsorbed kinetic energy into heat energy, and of then decreasing the load to a value equal to the weight of the airplane by further resisting the final load-producing movement thereof at a decreasing deceleration while converting the absorbed and the remaining unabsorbed kinetic energies into heat.

6. The method of absorbing and dissipating the kinetic energy of an airplane during landing by the combined action, of a resilient energy-absorbing medium and an energy-dissipating me-' dium carried by said airplane, comprising, the steps 0! building up in both media a maximum impact load, not substantially in excess of the maximum allowable impact load, during the initial load-producing movement of said airplane to an extent approximately equal to the deflection of said resilient medium for said built up maximum load, and of then decreasing the load during the remaining movement to a value equal to the weight of the airplane, by resisting the load-producing movement of the airplane while converting the unabsorbed and absorbed kinetic energies into heat energy. 1

- THEOPHILE 1m PORT. 

